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Bridgwater Tidal Barrier; EA submits Planning Application via Transport and Works Act

The Environment Agency has recently submitted its application to build the Bridgwater Tidal Barrier through the Transport and Works Act (TWA). Its rather like a planning application to Sedgemoor District Council but in this case its to the Secretary of State.

The EA TWA submission repeatedly sets out 10 objectives for this scheme and this article examines whether the Barrier we are being sold does what the EA and SDC say is on the tin.

DOES THE BRIDGWATER TIDAL BARRIER MEET ITS OBJECTIVES?

Description

The scheme consists of two elements designed to keep the sea out of Bridgwater town centre for the next 100 years. Dunball and Bristol Road have to take their chances if there is a breach where as Chilton Trinity gets a second level of protection.

Ultimately the EA plan is to hand over the existing downstream fresh water habitat to the sea creating an inter-tidal habitat. The effect will be to bring the coast from the Steart Peninsula up to Dunball converting the existing farmland to mudflats and salt marsh.

The BTB consists of two elements.

  1. 7 miles of improved river banks that will be maintained for 20 years after the construction of the BTB after which that maintenance will cease and the frequency of the saltwater inundation on the land will be allowed with increasing frequency and the freshwater habitat poisoned.

2. A large reinforced concrete structure with two lift gates located in unconventionally inland and exposed to salt water with a large tidal range that causes one of the most corrosive mechanisms for this type of structure.

The EA / SDC / SRA Objectives

These objectives are presented with no basis as to how they were arrived, what the pass fail criteria is and the implications of not meeting the objectives.

  1. Reduce tidal flood risk to the highest number of properties and commercial businesses in Bridgwater and the surrounding are
  2. Reduce tidal flood risk to critical infrastructure and utilities in Bridgwater and the surrounding area
  3. Deliver a scheme that can be adapted for the future effects of climate change.
  4. Align the project with the strategy set out in the PEFRMS (see also Section 2.2).
  5. Align the project with the recommendations set out in the ‘Protecting Bridgwater and the Somerset Levels & Moors from Tidal Flooding, Flood Risk Management Review’ (Black & Veatch, 2014) (see also Section 2.2).
  6. Ensure the design and operation of the scheme aligns with Local Plan policy for development and does not restrict the future development of Bridgwater and the surrounding area.
  7. Ensure the design and operation of the scheme aligns with Local Plan policy for development and does not restrict the future development of Bridgwater and the surrounding area.
  8. Minimise the impact on environmental receptors during the construction and operation of the scheme. Deliver mitigation as required to protect those receptors that may be affected, whilst maximising positive environmental outcomes.
  9. Minimise health, safety and welfare risks associated with the construction, and operation of the scheme.
  10. Identify funding and partnership opportunities and outline any additional work to gain financial contributions.
  11. Develop a sustainable scheme that minimises future operation and maintenance.

The Test

Objective No 3; Deliver a scheme that can be adapted for the future effects of climate change

It is not stated what those effects of climate change are believed to be, the reader is therefore wrongly invited to presume that the only effect will be rising sea level whilst ignoring other potential changes to the environment and what provisions for adaption have been included in the design as the statement implies.

To illustrate that the EA has not met its own objective I have the following observations.

  1. In order to support this statement, there would need to be a set of assumptions and the concept as to how it might be achieved.in order to judge whether the statement was correct, and the objective met . No such statement exists in the submission.
  2. The stated position of the EA/ SDC/ SRA is no pre-investment for a future scheme; there is no plan B or provision in terms of reserving space for the construction of a new barrier behind or in front of the proposed one.
  3. The TWA submission implies that the structure would  be useful beyond its design life of 100 years and quotes a 1:1,000 return period as being available for flood defense. The BTB is a reinforced concrete structure and in the saline (seawater) environment of the River Parrett such structures do not do well and it  is likely that structure would need to be replaced rather than adapted.
  4. The indicated clearance between the barrier gates when lifted  and the underside of the access bridge shows no provision for taller gates needed to accommodate rising sea level beyond the design basis.
  5. The planned abandonment of the downstream River Parrett riverbanks some 20 years after the barrier structure is completed means that  the  secondary flood defenses ultimately become the primary flood defence and the future shoreline close to Bridgwater. Much of these banks particularly  adjacent to the A38 are founded on the near liquid clay that underlay the Somerset Levels. Nearby Cannington Bends with similar ground conditions continues to settle and the submission notes the need for it to be made up every 30 years or so. It is worth noting that the trial embankment test results do not form part of the supporting documentation. Higher banks will increase the risk of settlement or a breach occurring and triggering an event that the scheme is meant to stop.

There is nothing within the TWA submission to support the statement that the objective has been considered, addressed or met.

Objective 7; Ensure the design and operation of the scheme aligns with Local Plan policy for development and does not restrict the future development of Bridgwater and the surrounding area.

Bridgwater if it maintains its present level of growth in housing and employment will need to increase its footprint by 40% during the design life of the BTB. Much of the allocated land in the present Local Plan approved in 2019 is already under development with only the new Gravity Development at Puriton providing substantial employment land. The only other low quality land available for housing and employment , around 1400 acres strategically close to Junction 23 will be used by the BTB as an operational flood plain to take seawater when barrier is in operation.

There is no statement explaining what Objective 7 actually means or how the objective is achieved.

Specifically this proposal


  1. Denies the Bridgwater the economic benefit associated with developing land adjacent to a motorway junction (J23).
  2. Denies Bridgwater the opportunity to build some 5000 houses and supporting employment centers
  3. Forces future housing development to the south west of Bridgwater that will continue to increase the demand on on the A39.
  4. Increases the separation between residential and employment centres with housing moving to the south and employment to the north ans as consequence increasing the amount of commuting and demand on the road system that ultimately restricts economic development.
  5. the SDC 2050 transport strategy shows the Northern Bridgwater Bypass crossing the operational flood plain created by this scheme. Roads creates economic development and the Transport Strategy and BTB appear to have conflicting objective for the land to north of Chilton Trinity.

In summary

The location of the Tidal Barrier ignores the expansion of Bridgwater over the next 100 years showing no consideration for the planned expansion of the town. There is nothing in the BTB submission to indicate what considerations have made. The EA/SDC decision not to commission an Economic Impact Assessment means that statement cannot be substantiated and explains the lack of a coherent position on objective 7. The Objective is clearly not met.